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We carried out two studies to test the hypothesis that genetic and environmental influences explain population group differences in general mental ability just as they do individual differences within a group. We estimated the heritability and environmentality of scores on the diagrammatic puzzles of the Raven's Coloured and/or Standard Progressive Matrices (CPM/SPM) from two independent twin samples and correlated these estimates with group differences on the same items. In Study 1, 199 pairs of 5-to 7-year-old monozygotic (MZ) and dizygotic (DZ) twins reared together provided estimates of heritability and environmentality for 36 puzzles from the CPM. These estimates correlated with the differences between the twins and 94 Serbian Roma (both rsZ0.32; NsZ36; ps!0.05). In Study 2, 152 pairs of adult MZ and DZ twins reared apart provided estimates of heritability and environmentality for 58 puzzles from the SPM. These estimates correlated with the differences among 11 diverse samples including (i) the reared-apart twins, (ii) another sample of Serbian Roma, and (iii) East Asian, White, South Asian, Coloured and Black high school and university students in South Africa. In 55 comparisons, group differences were more pronounced on the more heritable and on the more environmental items (mean rsZ0.40 and 0.47, respectively; NsZ58; ps!0.05). After controlling for measurement reliability and variance in item pass rates, the heritabilities still correlated with the group differences, although the environmentalities did not. Puzzles found relatively difficult (or easy) by the twins were those found relatively difficult (or easy) by the others (mean rZ0.87). These results suggest that population group differences are part of the normal variation expected within a universal human cognition.

Indigenous people are over-represented among the world's disadvantaged; their health is influenced by lack of access to critical resources including health care and by their cultural practices. We report on the health and the health practices of one group of indigenous women, the Roma/Gypsies of northern Serbia who live in poverty, reside in sub-standardized housing in segregated communities, and are poorly educated and stigmatized. We describe the environment in which they live, their health history, and the cultural practices that influence their health and health behaviors, including their sporadic utilization of health services that are provided by the state. We also present evidence supporting that, in the face of adversity, cultural practices, including those related to kinship and social support, can have significant benefits in shaping health status.

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This paper deals with a full range of sexual and reproductive behaviors among different "tribes" of Gypsies in Serbia. The examined traits include rates of fertility, mortality, age distribution, education, crime rates, and parental care. In addition, Gypsy traditions of culturally prescribed sexual behavior are also studied. It is found that Gypsy tribes employ different reproductive strategies, ranging from an extreme, for humans, "r" (reproductive) strategy to a more typical "K" (parental) strategy. The reasons bringing about these differences come from the Gypsies' readiness to adjust their behavior and reproduction in order to create the most favorable strategy in a given environment. This paper elucidates and contrasts the more typical r-selected Gypsies with a group of K-selected Gypsies living in a Serbian village.